pumped water
storage

Also known as pumped hydropower, a type of energy
storage and power generating facility that pumps water to a storage
reservoir during off-peak periods, and uses the stored water (by allowing
it to fall through a hydro turbine) to generate power during peak periods.
The pumping energy is typically supplied by lower cost base power capacity,
and the peaking power capacity is of greater value, even though there is
a net loss of power in the process.